A jig for calcining an electronic component is required to be unreactive with ceramic electronic components to be calcined in addition to having heat resistance and mechanical strength. When an electronic component work such as a dielectric is contacted and reacted with the calcination jig, a problem arises that the characteristics may be deteriorated due to the fusion or the composition fluctuation of the work.
The substrate for the jig for calcining the electronic component generally includes an alumina-based material, an alumina-mullite-based material, an alumina-zirconia-based material, an alumina-magnesia-based spinel material, an alumina-mullite-cordierite-based material and a combination thereof.
In order to prevent the contact of the jig with the work, a method of coating zirconia (zirconium oxide) on the surface layer is employed. Although the reactivity of the zirconia with the substrate is low, the coating of the jig may be cleaved or peeled off under an environment in which the repeated heat cycles take place due to the larger difference between thermal expansion coefficients of the substrate and the zirconia. When the jig is repeatedly used and the particles contained in the surface zirconia layer has a lower particle removal resistance or a lower abrasion resistance, the fine particles are mixed in electronic components to cause a severe problem.
The phase change from a monoclinic system to a tetragonal system takes place in the zirconia at around 1100° C. As a result, a problem arises that the change of the thermal expansion coefficient accompanied with the phase transformation due to the repeated heat cycles eliminates the coated layer of the zirconia to generate cracks so that electronic components to be calcined are likely to be influenced by the substrate.
In order to solve these problems, a jig for calcining an electronic component has been proposed in which an intermediate layer made of aluminum oxide (alumina) is disposed between the zirconia surface layer and the substrate. However, in the jig for calcining the electronic component, the sintered ability of the alumina acting as the intermediate layer is inferior and the alumina has only insufficient adhesion between the zirconia surface layer and the substrate. Accordingly, the jig has a defect that the peeling-off of the zirconia surface layer cannot be prevented against the thermal stress generated by the expansion and the contraction of the zirconia surface layer due to the heat cycles.
An application method, a dip-coating method and a spray-coating method are used for forming the zirconia layer (or zirconia film) on the substrate surface of the jig for calcining the electronic component. In these methods relatively inexpensive and suitable for industrial production, the anti-grain detaching property and the anti-abrasion property of the formed zirconia layer may be insufficient. Especially, under the circumstance in which the heat cycles are repeatedly loaded on the jig for calcining the electronic component, the zirconia layer may be peeled off from the substrate and the grains may be detached.
In order to overcome these defects, a jig for calcining an electronic component has been proposed in which a partially fused-bonding agent made of a metal oxide is added to a zirconia layer as shown in JP-A-2001-213666 (paragraph 0011) and JP-A-8(1996)-253381. For example, in JP-A-2001-213666, a jig for calcining an electronic component including a partially fused-bonding agent containing aluminum oxide (Al2O3) as an essential component into which one or more, and preferably two or more metal oxides selected from yttrium oxide (Y2O3), calcium oxide (CaO), magnesium oxide (MgO) and strontium oxide, (strontia, SrO) are added is disclosed.
The partially fused-bonding agent in the jig for calcining the electronic component binds coarse zirconia and/or fine zirconia to increase the strength and to elevate the adhesion with the substrate, thereby suppressing the peeling-off and the pulverization of the zirconia layer. Accordingly, the jig with the sufficient strength can be economically fabricated.
Since, however, the partially fused-bonding agent described in JP-A-2001-213666 contains the second, third or subsequent metal oxide as the essential component in addition to the essential aluminum oxide, the choice range is rather narrow so that the jig for calcining the electronic component containing the partially fused-bonding agent in which a wider range of metal oxides can be used has been requested.
In the jig for calcining the electronic component in which only the top surface of the substrate is coated with the zirconia, the contraction of the top surface of the substrate likely becomes larger than that of the bottom surface during the calcination and during the repeated use so that the substrate may be warped to generate a curvature. In order to overcome the problem, jigs for calcining electronic components have been proposed in which the bottom surface of the substrate is coated with the same zirconia in addition to the top surface thereof (JP-A-2002-37676, JP-A-2001-130084 and JP-B-3139962).
In the jig for calcining the electronic component having the three-layer structure having the zirconia on the top and bottom surfaces, the investigation with respect to the performance elevation is insufficient. Although the warp can be prevented, the other performance such as peel-off resistance has not bee sufficiently elucidated.